This invention relates to a process for clarifying milkhouse wastewater by removing phosphorus and suspended solids therefrom.
Dairy cows are milked twice daily and in a tie stall operation, the cows are milked in a stable. A vacuum pump draws the milk from the stable into a milkhouse through a glass pipeline. The milk is collected in a refrigerated storage tank and held there until collected by a milk transport truck.
Prior to each milking, a sanitizer is rinsed through the milking equipment and pipeline. Following milking, water is rinsed through the system to remove the remaining milk. This is followed by a detergent rinse through the system and finally, an acid rinse is washed through the system to prevent buildup of milk stone. A typical sanitizer for this purpose is sodium hypochlorite, while a typical detergent contains sodium hydroxide and sodium hypochlorite. The acid rinse normally includes phosphoric acid and sulphuric acid.
Between 500 and 1,000 liters of milkhouse waste are discharged from an average dairy farm each day. On farms with liquid manure systems, this water is stored with the manure in a concrete or earthen storage facility and spread during the summer months. However, on farms where manure is handled as a solid, other means must be found for disposing of the large volumes of liquid discharged from the milkhouse.
An obvious answer to the disposal of milkhouse wastewater would seem to be a septic system. Such systems are relatively inexpensive, require little operator attention and eliminate the need for spreading large volumes of liquids. However, buried septic systems are commonly known to have failed after being loaded with milkhouse wastewater for less than two years. An oily mat forms between the crushed stone and the native soil in the trenches and eventually this mat may become impermeable and cause the wastewater to back up through the system onto the milkhouse floor.
A further problem with milkhouse wastewater is its high phosphorus content. Since phosphoric acid is usually part of the acid rinse washed through the system to prevent milk stone buildup, the effluent from the milkhouse may contain phosphorus in substantial concentrations, e.g. up to 100 mg/l or more. However, phosphorus concentrations in excess of about 0.03 mg/l in the milkhouse wastewater may cause prolific growth of algae in surface waters. As bacteria digest the algae, they use dissolved oxygen from the water.